This invention relates to a method of making a laminated container consisting mainly of thermoplastic material, comprising the steps of first forming an outer container element and then forming an inner container element by blowing within said outer container element.
For many purposes it is desirable to use laminated containers made from materials which cannot be co-extruded.
This applies to e.g. food containers which should be impervious to volatile substances, radiation, etc.. When making such containers, it is desirable to combine a generally rather expensive plastics material possessing the necessary barrier properties with a cheaper material having suitable mechanical properties, e.g. polyethylene and polystyrene, and frequently such materials are incompatible.
It is well known to make a laminated thermoplastic container by a method comprising the steps of preparing a first container element of a thermoplastic material by conventional moulding, allowing said first container element to cool, positioning the cooled first container element in a holder and using said first container element as a mould for blow moulding a second container element within said first container element, the two container elements being united to form a laminated container during the blow moulding operation.
This known method is complicated and labour consuming and is unsuitable for automated production, because it is based on several separate operations.
Furthermore, this known method is based on the condition that the first container element can be transferred to and positioned in a holder in which the blow moulding of the second container element takes place. Thus, the first container element should have a minimum weight, thickness and/or rigidity. Thus, the selection of materials is limited when using said known method, and in order to fulfill the necessary conditions it may be necessary to use more thermoplastic material than actually required to obtain a container having the desired properties. Thus, in order to obtain satisfactory barrier properties, it is ordinarily sufficient to use an outer container element made from a thin film.